Shower base



FIG. 1 is a front elevated view showing an embodiment of the design;

FIG. 2 is a rear elevated view thereof;

FIG. 3 is a front view thereof;

FIG. 4 is a rear view thereof;

FIG. 5 is a side view thereof; and,

FIG. 6 is a top view thereof.

The broken lines included in the drawings are for the purpose ofillustrating a portion of the shower base that forms no part of theclaimed design.

The ornamental design for a shower base, as shown and described.